Fender Performer 1000 distortion channel

[52 Bill]

(i managed to work out CR39 being off explains the loss of my footswitch and CR49 the loss of Gain1).

Don't get ahead of yourself here. If you look at the schematic, the panel switch that changes from clean to dirty adds a reverse polarity diode in parallel to CR39. So if you want, retest CR39 and then switch the channel switch and see if it tests correctly.

I personally think that the switching will work again once the +16vdc is restored. It is possible that the cause of the low voltage is from something in the switching circuit.

There will only be dc voltage on the outputs of the ICs that are part of the switching circuit. All of the audio op amps are running with dual polarity supplies, so there should be little or no dc voltage on any output pin. If the op amps were only running on a single power supply like in a FX pedal, then there would be a bias voltage applied to the input and therefore would appear at the output pin. If there is an internal short in one of the ICs, then often there is a dc voltage that will show up on the output pin.

[showmaster78]

Update.
My amps dead!!!
Took out the suspect diodes and tested them, they were all bust.
So I've replaced them, put everything back together and now it keeps blowing fuses!!
I checked, double checked and checked everything again before i put it back together, and then triple checked before i switched it on. I seem to be getting a massive surge from somewher cos it dodnt just take out the F2A, it took out the fuse in the mains plug as well!! I have no idea whats gone wrong...

[showmaster78]

Ive found part of the problem. CR28 BLEW UP!!!

[showmaster78]

Right, more advice needed please.
It turns out what happened is that somehow a bit of terminal wire (like a resistor leg or something) got trapped against CP8 and CP9. I believe CP8 is a transformer connection, CP9 connects to the thermal switch on the power amp heat sink.
This has created a massive surge and caused CR28 to literally blow up. Now, i cant see any other damage and I've yet to test the other CRs in that circuit but what else will i need to test (presumably Q11-Q14 will need checking as well)?

[52 Bill]

This has created a massive surge and caused CR28 to literally blow up. Now, i cant see any other damage and I've yet to test the other CRs in that circuit but what else will i need to test (presumably Q11-Q14 will need checking as well)?

CR28 is part of the bias circuit, so if it has been damaged by some sort of surge, all of the transistors in the power amp will need to be tested.

It is unfortunate that this has happened, but it is not insurmountable. You need to methodically test all of the parts in the power amp and power supply. If you don't have one, build yourself a light bulb limiter, it will help when you get to the point of powering the amp on again.

[showmaster78]

Is that Q's 9-14?

[showmaster78]

Ok, so after extensive testing, ive found the following.
CR25 - 27 all reading short circuit (28 physically blew up so no point testing that one)
CR29 im getting 223o in flow direction, 300o in reverse.
CR30 - 36 are all good
CR37 - 38 short circuit.

Q9 an Q10 were fun ones. According to the specs they should be EBC config, but the readings were mixed up.
Q9. 001 B-C, 233 B-E and 301 C-E
Q10. 003 B-C, 065 B-E and 063 C-E
Q11 - 14 were all reading short circuit in all terminal combinations

So aside from replacing the known dead diodes and transistors, what else do i need to be doing at this stage?

[52 Bill]

You will need to test the shorted diodes and transistors again once that have been removed from the circuit. There are parallel paths so one shorted diode may make other diodes or transistors test as shorted while still in circuit.

Before you completely remove any diode, just unsolder one end and then test it again with your meter. If it still reads as a short, remove it. If it reads okay, then just leave it hanging until you test the rest of them. Once you have found all of the bad ones, go back and solder them all back in along with the new ones at the same time.

One thing to watch for is to double check your soldering. Leaving solder bridges on the pc board will really spoil you day.

[showmaster78]

Yeh i took the rectifiers out of circuit (I had to with the diodes anyway, i couldnt get in to test them with them being inside the heatsink. The TIP142/147 I just disconnected the base) and they were all reading shorted. As there are only 2 other diodes reading shorted and only 2 other transistors in the circit, for the sake of £5 for the entire repair I'm just gonna change them all to ensure reliability.
Is there anything else i need to test before i do this?

[52 Bill]

Is there anything else i need to test before i do this?

It seems that you have tested everything except the input chip U7, and there is no easy test for that other than reading voltages or substitution.

Do any of the power amp resistors show signs of overheating or burning?

[showmaster78]

The 2x120ohm resistors get really hot but I've checked the condition of the board, solder joints and measured the voltages running through them, all seems fine.
Dunno if anyone knows the answer to this, but if my multimeters lowest resistance setting is 20ohm, how low should it be able to read? Im asking because i checked all the resistors in the power rails but the .47ohm are all reading 1ohm. I dont know i its just that my multimeter cant read any lower or they are, for some very strange reason, providing a 1ohm resistance?

As for U7, I'll need to get the output circuit and rectifier rail back in order to be able to check it since it just fries fuses as soon as i turn the switch on now...

[DrGonz78]

Dunno if anyone knows the answer to this, but if my multimeters lowest resistance setting is 20ohm, how low should it be able to read? Im asking because i checked all the resistors in the power rails but the .47ohm are all reading 1ohm. I dont know i its just that my multimeter cant read any lower or they are, for some very strange reason, providing a 1ohm resistance?

Main thing about those 0.47ohm resistors is that they are not reading open or even measuring way over 1 ohm resistance. Measure the resistance of your meter probes directly together and you get 0.3 to 0.6 ohms resistance just in your probes alone. Add that 0.3-0.6 ohms resistance to anything your measuring for even more accuracy.

[showmaster78]

So that suggests your saying they are most likely fine. Thats a load off lol.
So, next step is to replace the shit that has (i think) shorted out and then attack the IC.
Now, since its frying fuses, looking at the schematic it looks like the fuse is in the feed from the rectifier circuit. I hope to god thats the case and the circuit is just letting rogue currents through. If its going the other way it suggests there is still a short...
So is there likely to be anything else (transformer or something) that could overload the circuit once all the output stage is fresh and new?

[52 Bill]

Now, since its frying fuses, looking at the schematic it looks like the fuse is in the feed from the rectifier circuit. I hope to god thats the case and the circuit is just letting rogue currents through. If its going the other way it suggests there is still a short...
So is there likely to be anything else (transformer or something) that could overload the circuit once all the output stage is fresh and new?

The fuse is in the primary ac circuit of the transformer, meaning that it will blow if there is a problem with the transformer or with the power supply or with the power amp circuit, etc.

Test all of the power supply diodes CR52-CR55 if you haven't already done so.

Are you powering the amp up with all of the dead parts removed? Something that you should know about this series of amps is that you should never power up the amp with the board floating, unattached to the heatsink bar and chassis. Even for short periods of testing.

I strongly suggest using a light bulb limiter when you next power up the amp. And disconnect the speaker from the circuit until you know that there is no dc on the output buss.

[showmaster78]

The fuse is in the primary ac circuit of the transformer, meaning that it will blow if there is a problem with the transformer or with the power supply or with the power amp circuit, etc.

Test all of the power supply diodes CR52-CR55 if you haven't already done so.

Are you powering the amp up with all of the dead parts removed? Something that you should know about this series of amps is that you should never power up the amp with the board floating, unattached to the heatsink bar and chassis. Even for short periods of testing.

I strongly suggest using a light bulb limiter when you next power up the amp. And disconnect the speaker from the circuit until you know that there is no dc on the output buss.

I havent tested those diodes yet. I meant to and for some reason it slipped my mind.

As for powering up with bits removed, i know i somehow missed a wire causing a short circuit but only a phsycopath would power up with the board out and diodes removed, surely?

No, when i said about the fuses, it blew them the first time because of the short circuit so i replaced them, cleared the short and powered up again. Same result. The only thing that was in any way unfastened was the chassis from the cab. Everything else was wired up and bolted down.
Except the reverb, but the tank was bust when i got the amp and its been fine without it. Its the other things that have caused the issues. Should have just left it as a clean only amp and got some stomp boxes lol